1. Field of the Invention
The present invention relates to an exposure method with a plurality of light beams to record or read an image by causing the plurality of light beams to scan two-dimensionally.
2. Description of the Related Art
An image recording apparatus for subjecting an original to slit exposure and recording an image on an image recording material such as a photosensitive material is known. An illustrative example of the image recording apparatus includes an image recording apparatus wherein two kinds of image recording materials, i.e., a photosensitive material and an image receiving material are used and an image on the exposed photosensitive material is transferred onto the image-receiving material by a thermal development/transfer process thereby processing the image.
In the thermal development/transfer type image recording apparatus, the photosensitive material and the image receiving material are respectively wound and accommodated in roll form within magazines the insides of which are in light-intransmissive states. The materials are used by being successively pulled out from their respective magazines for each image recording process. Further, the image recording apparatus is provided with a thermal development/transfer unit. Slit images on an original are successively exposed onto the photosensitive material which is drawn a predetermined length from the magazine and cut while the photosensitive material is being nipped and conveyed by conveying rollers. Thereafter, the photosensitive material is conveyed to the thermal development/transfer unit. On the other hand, the image receiving material is pulled out a predetermined length from the magazine and cut in a manner similar to the photosensitive material. Thereafter, the image receiving material is delivered into the thermal development/transfer unit by the conveying rollers in synchronism with the conveyance of the photosensitive material. In the thermal development/transfer unit, the photosensitive material is thermally developed while being nipped and conveyed in a state superimposed on the image receiving material so as to transfer an image onto the image receiving material. Thus, a desired image is recorded on the image receiving material.
In the image recording apparatus referred to above, there is known an image recording apparatus which main-scans with light beams such as laser beams in one direction and sub-scans simultaneously or successively with the main scanning to convey a photosensitive material in a direction intersecting the direction of the main scanning and forms a color image onto the photosensitive material.
In this type of image recording apparatus, three-color laser beams are combined into one laser beam and the photosensitive material is exposed by being main-scanned and sub-scanned with the combined laser beam.
Since the above image recording apparatus requires an image recording with no color variations and has high color reproduction, laser beams of three colors produced by image data at a certain portion should be exposed onto the same portion on the photosensitive material. Therefore, there is proposed an image recording apparatus for combining the three color laser beams into one laser beam group on an optical path of an optical system prior to the scan optical system referred to above and exposing a photosensitive material by scanning it with the one laser beam.
However, in this type of image recording apparatus, an adjusting device is complex in structure and fine adjustment is required to bring the three laser beams into the same state, i.e., a state converged in the same direction and in the form of the same beam on the same optical path.
Even if the optical system is adjusted as described above, points to be adjusted are often shifted or displaced due to vibrations produced when the image recording apparatus is conveyed or moved. As a result, the complex and fine adjustment of the optical system must be made again. Further, the points to be adjusted in the optical system are often displaced due to a secular change in the apparatus. Therefore, such points are under the necessity of readjustment.